In conventional fuel pumping systems for internal combustion engines such as a diesel engine, remotely disposed fuel pumps communicate with an injection valve located in the head of each engine cylinder by means of fuel lines. While such systems operate effectively in small capacity engines operating under normal load conditions, such systems are less effective when engine rpm and mean effective pressures are increased.
The relatively wide spacing between the pump and injector valve accommodates a relatively large volume of fuel which is subject to sizable variations in pressure and temperature and because the fuel has some compressibility and the speed of pressure impulses is limited to the speed of sound may cause difficulties such as the substantial time lag between the pumping action and the actual injection of the fuel into the cylinder. To remedy this latter problem, it is usually necessary to provide a sophisticated timing advance mechanism to achieve efficient fuel injection at varying engine speeds.
The unit injector, a device which broadly includes a high pressure fuel pump and injector mechanism in the same housing attached to the combustion chamber of the engine with which it is associated, has been developed to overcome the above-noted disadvantages of the conventional systems. By utilizing a low pressure fluid transfer mechanism for fuel metering and speed control, the instant unit injector can accurately, and with a minimum of expensively machined apparatus, achieve high pressure injection of fuel into the engine cylinder with improved control of injection and with precise timing.
Representative of some prior art attempts to deal with related difficulties are U.S. Pat. No. 2,898,051; 2,985,378; 3,075,707 to Teichert, Falberg, and Rademaker respectively. None of these patents, however, teaches the particular utilization of an unrestrained free-floating plunger disposed between a power piston and an injector valve as engrossed by the present invention.